More pictures and projects today!

What could be the culprit behind these yellow leaves?

380 ppm, 5.8, 85-90F, 85+F res temps
Now with the ac ducted I shouldn't have a problem with temps outside of the res and hopefully will in turn lower res temps. If not it's back to the store to pickup some of those freeze packs. How many do you recommend in order to lower 10-15 gallons of water 10 degrees F?

Thanks!